As air travel has increased over the past decades, airport facilities have become more crowded and congested. Minimizing the time between the arrival of an aircraft and its departure to maintain an airline's flight schedule, and also to make a gate or parking location available without delay to an incoming aircraft, has become a high priority in the management of airport ground operations. The safe and efficient ground movement of a large number of aircraft simultaneously into and out of ramp and gate areas has become increasingly important. As airline fuel costs and safety concerns and regulations have increased, the airline industry is beginning to acknowledge that continuing to use an aircraft's main engines to move aircraft during ground operations is no longer the best option. The delays, costs, and other challenges to timely and efficient aircraft pushback from airport terminals associated with the use of tugs and tow vehicles makes this type of aircraft ground movement an unattractive alternative to the use of an aircraft's main engines to move an aircraft on the ground. Restricted use of an aircraft's engines on low power during arrival at or departure from a gate is an additional, although problematic, option. Not only does such engine use consume fuel, it is also burns fuel inefficiently and produces engine exhaust that contains microparticles and other products of incomplete combustion. Operating aircraft engines, moreover, are noisy, and the associated safety hazards of jet blast and engine ingestion in congested gate and ramp areas are significant concerns that cannot be overlooked.
The use of a drive means, such as a motor structure, integrally mounted with a wheel to rotate the wheel of an aircraft has been proposed. The use of such a structure should move an aircraft independently and efficiently on the ground without reliance on the aircraft's main engines. U.S. Pat. No. 2,430,163 to Dever; U.S. Pat. No. 3,977,631 to Jenny; and U.S. Pat. No. 7,226,018 to Sullivan, for example, describe various drive means and motors intended to drive aircraft during ground operations. None of the foregoing patents, however, suggests a roller traction or like drive mechanism activated by a clutch to actuate drive means intended to move an aircraft independently and efficiently on the ground.
U.S. Pat. No. 7,469,858 to Edelson; U.S. Pat. No. 7,891,609 to Cox; U.S. Pat. No. 7,975,960 to Cox; and U.S. Pat. No. 8,109,463 to Cox et al., owned in common with the present invention, describe aircraft drive systems that use electric drive motors to power aircraft wheels and move an aircraft on the ground without reliance on aircraft main engines or external vehicles. While the drive means described in these patents and applications can effectively move an aircraft autonomously during ground operations, it is not suggested that the drive means could be driven or actuated by clutch-activated roller traction or like drive systems. None of the foregoing art, moreover, recognizes the significant improvements in drive means operating efficiency possible when gearing systems are replaced by clutch-activated roller traction or similar drive systems to actuate drive means that move aircraft autonomously during ground operations.
The drive means currently proposed to drive aircraft on the ground typically rely on gearing systems that operate with the drive means to drive an aircraft wheel and, thus, the aircraft. Traction drives, such as that described in U.S. Pat. No. 4,617,838 to Anderson, available from Nastec, Inc. of Cleveland, Ohio, which relies on ball bearings, can be used to replace gears in some contexts. Adapting roller or traction drive systems to replace gearing and/or gear systems in an aircraft drive wheel to actuate drive means that independently drive an aircraft drive wheel has not been suggested, nor has the use of a clutch assembly to activate such roller traction drive systems been mentioned.
Many types of vehicle clutch assemblies are well known in the art. U.S. Pat. No. 3,075,623 to Lund; U.S. Pat. No. 3,599,767 to Soderquist; and U.S. Pat. No. 7,661,329 to Cali et al, for example, describe clutch assemblies incorporating sprag or pawl elements that may transmit torque between races or rotatable elements depending, in part, on their relative directions of rotation. Neither these clutch designs nor other commonly available similar clutch designs are sufficiently robust to function effectively and reliably in an aircraft drive wheel system to engage a drive system and actuate a drive means as required to drive an aircraft autonomously during ground operations. McCoskey et al. suggests a dual activated cone mechanism or a reverse sprag mechanism that may be used when overrunning in forward and locking in reverse is desired in connection with wheel motors in a powered nose aircraft wheel system in U.S. Pat. No. 7,445,178. McCoskey et al. does not teach a safe overrunning bidirectional clutch assembly for an aircraft drive wheel drive system that includes sprag or pawl elements designed and configured to prevent improper engagement of the clutch assembly when an aircraft is driven independently on the ground.
A need exists, therefore, for an effective and reliable clutch assembly with engagement elements having configurations specifically designed to selectively engage and transfer torque to an aircraft drive wheel roller traction or other drive system with a highly efficient drive system-actuated non-engine drive means that drives an aircraft drive wheel to move the aircraft autonomously on the ground without reliance on the aircraft's main engines or external ground vehicles.